This invention relates to a navigation apparatus for a vehicle which uses a GPS (Global Positioning System) receiver as a sensing means to display on a display section information on the basis of sensed results such as a present position, a running locus and the like.
In the conventional navigation apparatus for a vehicle of this kind, information such as a present position, a running locus and the like on the basis of sensed results by the GPS receiver are displayed by a predetermined marker and a predetermined bright line on a map displayed on an image plane of a display section.
When a vehicle passes through a ravine, between buildings, through a tunnel or the like which cannot receive radio waves from the artificial satellite, the GPS receiver cannot effect sensing.
In such a case, a final position sensed continues to be displayed on the display section in the same form.
In the conventional navigation apparatus for a vehicle, in the case where the GPS receiver can no longer effect sensing because the former cannot receive radio waves from the artificial satellite, the final present position displayed on the display section continues to be displayed. This poses an inconvenience in that a user may not notice that the present position marker on the display section has stopped. Thus, the user sometimes fails to recognize an actual running position and an adequate (sufficient) running guide cannot always be given to the user.
Particularly, the navigation apparatus for a vehicle of this kind uses a display section having a relatively small display image plane. Therefore, in the case where the vehicle runs at a normal speed, although the display point indicating a present position on the display section moves, movement of the display point cannot be recognized immediately. Thus, the user may not become aware of a discrepancy between the actual running position and the present position displayed on the display section until after much time has passed.
This invention has as objects overcoming the aforementioned inconveniences and providing a navigation apparatus for a vehicle which can immediately confirm on the basis of a variation of a display state of a present position on the display section that movement of the present position has stopped, and which can prevent an actual running present position from being mistaken.
Furthermore, in the conventional navigation apparatus, it is contemplated that the GPS receiver becomes incapable of performing sensing either when the number of artificial satellites capable of receiving radio waves is small, or when the vehicle passes through a ravine, between buildings, through a tunnel or the like, and therefore becomes incapable of receiving radio waves from the artificial satellite even though the number of artificial satellites capable of receiving radio waves is sufficient.
In such a case, displaying of information such as a present position, a running locus and the like is discontinued and, instead, information such as a final present position sensed on the image plane of the display section or the running locus to the final present position continues to be displayed on the display section.
In the conventional navigation apparatus for a vehicle, when the GPS receiver becomes incapable of performing sensing, the final present position displayed on the image plane of the display section does not move but remains stationary, and the running locus remains unchanged.
Judgment is not made that such a state results from the small number of artificial satellites capable of receiving radio waves or results from the radio waves from the artificial satellites being cut off despite there being a sufficient number of artificial satellites. This poses inconveniences in that the final present position or the running locus to the final present position continues to be displayed, which causes the user (a driver) to mistake a running position. Alternatively, it poses the problem that a user may mistakenly believe that the number of artificial satellites capable of receiving radio waves is insufficient, even though the cause is merely a transient cut off of radio waves. As a result, the user would turn off the power source of the navigation apparatus for a vehicle, even though the lack of reception is merely transient.
Another object of the invention is to overcome the aforementioned inconveniences and further to provide a navigation apparatus for a vehicle which can precisely inform the user of the fact that sensing is impossible due to a shortage in the number of artificial satellites capable of receiving radio waves, or that sensing is impossible because, even though the number of artificial satellites capable of receiving radio waves is sufficient, radio waves from the artificial satellites are temporarily cut off.